I once met a person that never drank water, only soft drinks. It’s not the unhealthiness of this that disturbed me, but the fact they did it without the requisite paperwork.
Unlike those disorganised people I have a formal waiver. I primarily drink steam and crushed glaciers.
A lot of phone modems ship with their own SoC (processor) running its own OS. It’s much smaller and slower than the main phone SoC but, depending on its implementation, it can have full access to all of your main processor’s memory through DMA.
Anything odd with temperatures or power draws perhaps? nv-top shows both for me (but I run an AMD GPU + non-proprietary drivers), otherwise lm-sensors might be good.
Neither the GPU nor CPU utilisation change at the 30 min mark? If one is pegged at 100% then it’s probably hard to work out what is going on. Running a singleplayer game staring at a wall and configured with limited framrate might let you run both the CPU and GPU at less than 100%, perhaps making it easier to see if one or the other suddenly changes.